1. Field of the Invention
The present invention generally relates to a method of forming tungsten layers and, more particularly forming tungsten layers using a pulsed nucleation deposition process.
2. Description of the Related Art
Integrated circuits have evolved into complex devices that can include millions of components (e.g., transistors, capacitors and resistors) on a single chip. The evolution of chip designs continually requires faster circuitry and greater circuit density. The demands for greater circuit density necessitate a reduction in the dimensions of the integrated circuit components as well as improved layer uniformity.
In particular, metal layers, such as those used for interconnect, contact, and plug fill applications, are subject to increasingly stringent requirements related to step coverage and layer uniformity. Tungsten layers, for example, are particularly difficult to deposit with uniform step coverage. Typically, tungsten layers are formed by chemical vapor deposition (CVD), using a two step process. A bulk tungsten layer is typically deposited by reacting tungsten hexafluoride (WF6) with hydrogen (H2) on a substrate. In order to reduce the time required to initiate the reaction between the tungsten hexafluoride (WF6) and the hydrogen (H2) (i.e., reduce the “incubation time”), a nucleation layer is typically deposited prior to depositing the bulk tungsten layer. Unfortunately, the nucleation layer, typically deposited by reacting tungsten hexafluoride (WF6) with silane (SiH4), has sub-optimal step coverage. As a result, voids may form in the tungsten nucleation layer during deposition, adversely impacting the electrical performance of devices fabricated therefrom.
Therefore, a need exists in the art for a method of depositing a tungsten nucleation layer with improved step coverage.